1. Field of the Invention
The present invention relates to medical stents and methods of manufacturing the same. In particular, the present invention relates to medical stents with valves for preventing harmful gastric acid reflux in a patient.
2. Background of the Invention
Medical stents are generally flexible, tubular, expandable bodies formed of a plurality of interconnecting wires. The stents are used in a wide variety of medical applications, such as treatment of esophageal diseases or reinforcing constricted blood vessels or urinary tracts. The stent is usually placed into a constricted portion of a patient""s body using a delivery system, e.g. a catheter.
When a medical stent is used for treatment of an esophageal disease, such as esophageal tumor or stricture, the stent is placed at the lesion within the esophagus to maintain the esophageal lumen open. If the tumor or stricture is located near the junction between the stomach and the esophagus, the esophageal stent is often implanted across the lower esophageal sphincter (i.e. the ring-like muscle that constricts and relaxes the esophagus as required by normal physiological functions). However, the implantation of a stent across the normally-closed esophageal sphincter may hold the sphincter open unintentionally and cause harmful gastric acid reflux from the stomach into the esophagus.
In order to reduce the gastric acid reflux, it has been proposed to use an anti-reflux valve with an esophageal stent. An example of esophageal stent with an anti-reflux valve is disclosed by Kxc3x6cher et al. (xe2x80x9cEsophageal Stent with Antireflux Valve for Tumors Involving the Cardia: Work in Progress,xe2x80x9d JVIR 1998; 9:1007-1010). The anti-reflux valve of Kxc3x6cher et al. is made of a pliable, soft polyurethane sleeve attached to the lower end of the stent. However, there are several problems associated with this type of stent. For example, the sleeve must be long enough to prevent the reflux and act as a barrier wall to defeat capillary flow of acid up the bore of the device. Since the sleeve must be long, greater deployment force and more complex delivery catheter designs are required. Typically, the length of the sleeve ranges from about 50 to 120 mm and requires extra length on the delivery system to envelope it in the xe2x80x9cfoldedxe2x80x9d condition prior to deployment. In addition, the sleeve may become twisted, tangled, or kinked, which may inhibit the passage of food into the stomach. The sleeve also may become reversed and pushed up into the esophagus during vomiting. In that case, it may be difficult for the sleeve to return to its properly functioning position.
To overcome the drawbacks of the prior art and in accordance with the purposes of the invention, as embodied and broadly described herein, one aspect of the invention provides an esophageal medical stent having a rigid but elastic valve formed, preferably, near a distal end portion of the stent. The valve is normally closed but configured to open in response to a predetermined condition. For an esophageal stent, the predetermined condition may be a pressure difference between the upstream and the downstream of the valve. The normally closed valve then allows easy opening of the valve when the pressure difference exceeds a predetermined threshold value. For instance, a passage of food from the esophagus into the stomach causes the pressure difference across the valve large enough to open the valve and, upon completion of the food passage, the valve returns to its normal-closed state to prevent the reflux. A reverse backflow due to, for example, vomiting, which causes a large pressure difference, may also be permitted by configuring the valve with an appropriate threshold value for the reverse backflow.
According to another aspect of the present invention, the esophageal stent of the present invention may also be used for treatment of the gastroesophageal reflux disease (GERD). GERD is a frequent backflow of harmful gastric acid from the stomach into the esophagus. When the lower esophageal sphincter inadvertently relaxes at inappropriate times, e.g. after meals, it allows acid and food particles to reflux back into the esophagus. Although most of the reflux contents return back to the stomach, the remaining gastric acid reflux irritates the wall of the esophagus and produces discomfort or pain known as heartburn. GERD, however, is a medical condition when such reflux is frequent or severe enough to cause more significant problems. In order to treat GERD, a stent having an anti-reflux valve of the present invention can be placed in the lower esophagus to prevent the harmful gastric acid reflux.
Another aspect of the present invention, therefore, is to provide a method of manufacturing a medical stent having an valve. The method includes: providing a generally tubular body formed of braided wires and having a proximal end portion and a distal end portion; extending the braided wires near the distal end portion; and deforming the extended wires to form the valve, wherein the valve is configured to be normally closed and to be open in response to a predetermined condition. The valve is formed basket-shaped and at least a portion of the valve and/or at least a portion of the tubular body are provided with a suitable covering material.
Another aspect of the present invention is to provide a method of manufacturing a medical stent having an elastomeric valve. The method includes: providing a generally tubular body; positioning a fixture proximate to a portion of the tubular body; applying an elastomeric material onto the fixture; and removing the fixture to form the elastomeric valve, wherein the elastomeric valve is configured to be normally closed and to be open in response to a predetermined condition.
In yet another aspect of the present invention, a method of manufacturing a medical stent having a gasket valve includes: providing a generally tubular body; and attaching an elastomeric gasket valve integral to a portion of the tubular body, wherein the integral gasket valve is configured to be normally closed and to be open in response to a predetermined condition.
In still another aspect of the present invention, a medical stent comprises: a generally tubular body formed of braided wires and having a proximal end portion and a distal end portion; and a normally closed valve formed from the braided wires extended from the distal end portion, wherein the valve is configured to open in response to a predetermined condition. The valve is a basket-shaped spring valve, and at least a portion of the tubular body and/or the valve is provided with a suitable covering material.
In still another aspect of the present invention, a medical stent comprises: a generally tubular body having a proximal end portion and a distal end portion; and a normally closed valve made of an elastomeric material and formed integral to the distal portion of the tubular body, wherein the elastomeric valve is configured to open in response to a predetermined condition. The elastomeric valve is basket-shaped, and at least a portion of the tubular body and/or the valve is provided with a suitable covering material.
Additional objects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention will be realized and attained by means of the elements and combinations particularly pointed out in the appended claims.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention, as claimed.